From 320cb03b1f8bc324227f20e942b6459000a86c82 Mon Sep 17 00:00:00 2001
From: Dan Barber <github@danbarber.me>
Date: Fri, 23 Mar 2018 12:01:07 -0400
Subject: [PATCH] Add tests for king in check

---
 lib/chess/board.ex              | 12 ++++++++++
 lib/chess/moves/piece.ex        |  4 ++++
 test/chess/board_test.exs       | 40 +++++++++++++++++++++++++++++++--
 test/chess/moves/piece_test.exs |  9 ++++++++
 4 files changed, 63 insertions(+), 2 deletions(-)

diff --git a/lib/chess/board.ex b/lib/chess/board.ex
index 1157ac2..b764522 100644
--- a/lib/chess/board.ex
+++ b/lib/chess/board.ex
@@ -1,6 +1,8 @@
 defmodule Chess.Board do
   @moduledoc false
 
+  alias Chess.Moves.Piece
+
   def transform(board) do
     Enum.map(0..7, fn (rank) ->
       Enum.map(0..7, fn (file) ->
@@ -30,6 +32,16 @@ defmodule Chess.Board do
     Map.put(board, "#{to_file},#{to_rank}", piece)
   end
 
+  def check?(board, colour) do
+    king =
+      board
+      |> search(%{"type" => "king", "colour" => colour})
+      |> List.first
+
+    board
+    |> Piece.attacked?(king)
+  end
+
   def default do
     %{
       "0,7" => %{"type" => "rook",   "colour" => "black"},
diff --git a/lib/chess/moves/piece.ex b/lib/chess/moves/piece.ex
index fb8cc30..3c75381 100644
--- a/lib/chess/moves/piece.ex
+++ b/lib/chess/moves/piece.ex
@@ -49,6 +49,10 @@ defmodule Chess.Moves.Piece do
     Enum.any?(moves, &(match_piece(board, &1, "pawn")))
   end
 
+  defp _attacked?(_board, {0, _rank}, {-1, _}, _), do: false
+  defp _attacked?(_board, {_file, 0}, {_, -1}, _), do: false
+  defp _attacked?(_board, {7, _rank}, {1, _}, _), do: false
+  defp _attacked?(_board, {_file, 7}, {_, 1}, _), do: false
   defp _attacked?(board, {file, rank}, {fv, rv}, pieces) do
     {file, rank} =
       board
diff --git a/test/chess/board_test.exs b/test/chess/board_test.exs
index 0215798..c19f448 100644
--- a/test/chess/board_test.exs
+++ b/test/chess/board_test.exs
@@ -31,13 +31,49 @@ defmodule Chess.BoardTest do
 
   test "moves a piece" do
     board = %{
-      "3,0" => %{"type" => "queen",  "colour" => "white"},
+      "3,0" => %{"type" => "queen", "colour" => "white"},
     }
 
     new_board = Board.move_piece(board, %{"from" => [3, 0], "to" => [5, 2]})
 
     assert new_board == %{
-      "5,2" => %{"type" => "queen",  "colour" => "white"},
+      "5,2" => %{"type" => "queen", "colour" => "white"},
     }
   end
+
+  test "recognise when the king is in check" do
+    board = %{
+      "4,0" => %{"type" => "king", "colour" => "white"},
+      "4,7" => %{"type" => "queen", "colour" => "black"},
+    }
+
+    assert Board.check?(board, "white")
+  end
+
+  test "recognise when the king is not in check" do
+    board = %{
+      "5,0" => %{"type" => "king", "colour" => "white"},
+      "4,7" => %{"type" => "queen", "colour" => "black"},
+    }
+
+    refute Board.check?(board, "white")
+  end
+
+  test "recognize when the king is in check by a knight" do
+    board = %{
+      "4,0" => %{"type" => "king", "colour" => "white"},
+      "3,2" => %{"type" => "knight", "colour" => "black"},
+    }
+
+    assert Board.check?(board, "white")
+  end
+
+  test "recognize when the king is in check by a pawn" do
+    board = %{
+      "4,0" => %{"type" => "king", "colour" => "white"},
+      "3,1" => %{"type" => "pawn", "colour" => "black"},
+    }
+
+    assert Board.check?(board, "white")
+  end
 end
diff --git a/test/chess/moves/piece_test.exs b/test/chess/moves/piece_test.exs
index 8b20e4d..9fa6376 100644
--- a/test/chess/moves/piece_test.exs
+++ b/test/chess/moves/piece_test.exs
@@ -12,6 +12,15 @@ defmodule Chess.Moves.PieceTest do
     refute Piece.attacked?(board, {4, 5})
   end
 
+  test "piece on the edge of the board is not being attacked" do
+    board = %{
+      "4,0" => %{"type" => "king", "colour" => "white"},
+      "2,7" => %{"type" => "rook", "colour" => "black"},
+    }
+
+    refute Piece.attacked?(board, {4, 0})
+  end
+
   test "piece is not being attacked by piece of its own colour" do
     board = %{
       "4,5" => %{"type" => "king", "colour" => "white"},